lock: do not encode result of gethostname on Python 2

If a hostname contained non-ascii character, str.encode() would first try
to decode it to a unicode and raise UnicodeDecodeError.

mercurial/lock.py

@@ -28,8 +28,9 b' def _getlockprefix():'
     confidence. Typically it's just hostname. On modern linux, we include an
     extra Linux-specific pid namespace identifier.
     """
-    result = socket.gethostname().encode(
-        pycompat.sysstr(encoding.encoding), 'replace')
+    result = socket.gethostname()
+    if pycompat.ispy3:
+        result = result.encode(pycompat.sysstr(encoding.encoding), 'replace')
     if pycompat.sysplatform.startswith('linux'):
         try:
             result += '/%x' % os.stat('/proc/self/ns/pid').st_ino